This invention relates generally to a stapler and, more particularly, to an improved stapler having an anvil structure that joins materials by flaring the legs of the staple outward and away from each other.
There are numerous applications in which staplers are used to clinch materials together by diverging and curling the legs of a staple outward and away from each other. Examples of such staplers are shown and described in U.S. Pat. Nos. 4,574,992 and 3,807,619. Referring to FIG. 1 herein, in one known application in the bedding industry, a fabric material 40 is clinched to a foam substrate 42 using a stapling process in which legs 44 of a generally U-shaped staple 46 are caused to flare or diverge and curl away from each other. The flare is accomplished with a known nose piece 20 that mounts in a known manner to a standard stapler 50, for example, a pneumatic stapler type VA0285 commercially available from Vertex Fasteners, Inc. of Skokie, Ill. The known nose piece 20 is an assembly comprised of an anvil 22 that is mounted with respect to a retaining block 24 by means of a pin 26 and a biasing element 28, for example, an anvil spring such as a compression spring. The retaining block 24 is attached to a backing plate 30 by means of fasteners 32. The anvil 22 has an angled guide or wedge 34 disposed on an anvil forward surface 27 adjacent a downstream, lower end 31 of the anvil 22. The wedge 34 has an upstream, thinner edge 52 and a downstream, thicker edge 67. The anvil spring 28 applies a biasing force against an anvil rearward surface 29 to push the thicker edge 67 of the wedge 34 against the backing plate 30.
In operation, a driver blade 36 has a proximal end mechanically connected to, and receiving a force from, an actuator 58, for example, a pneumatic cylinder, in a known manner. As shown in FIGS. 1 and 2A, an opposite, distal end 38 of the driver blade 36 contacts a crown 48 joining common ends of the two legs 44 of the staple 46. The driver blade 36 pushes the staple 46 between the backing plate 30 and the anvil 22. An upstream, thinner edge 52 of the wedge 34 has corner chamfers 54, 56; and as the staple legs 44 contact the spaced-apart chamfers 54, 56, they are deflected or guided outward and away from each other as they enter the materials being stapled. As the driver blade 36 continues to push the staple crown 48 between the backing plate 30 and the anvil 22, the staple crown 48 contacts the wedge 34. As shown in FIG. 2B, continued motion by the driver blade 36 forces the anvil 22 to compress the anvil spring 28 and move from left to right, as viewed in FIGS. 1 and 2B, along the pin 26. That motion permits the driver blade 36 to push the staple crown 48 past the wedge 34 and against the materials being fastened. The staple legs 44 continue to diverge and curl as they move through the foam substrate 42 (FIG. 1).
While the above nose piece 20 works satisfactorily in many applications, it does have disadvantages. First, many pneumatic staplers use a single acting cylinder 58 to apply the longitudinal drive forces on the driver blade 36. With a single acting cylinder 58, pressurized air from a source 60 is ported into one end 62 of the cylinder 58 and applies a force against a piston 64 mechanically connected to the driver blade 36. The pressurized air moves the piston 64 from left to right, as viewed in FIG. 1, and advances the driver blade 36 against the staple 46. As the piston advances through the cylinder, air stored in an opposite end 66 of the cylinder 58 is compressed. At the end of the staple drive stroke, that compressed air is used to return the piston 64 and retract the driver blade 36 to their respective starting positions. The return force produced by the compressed air to power the driver blade return stroke is substantially less than the force applied by the pressurized air from the source 60 during the driver blade drive stroke.
In operation, as shown in FIG. 2C, after the driver blade 36 pushes the staple 46 over a downstream, larger end 67 of the wedge 34, the driver blade 36 is then squeezed between the thicker edge 67 of the wedge and the backing plate 30 by the force of the anvil spring 28. Thus, a longitudinal force required to retract the driver blade 36 must be sufficient to overcome the side force imposed by the anvil spring 28. On occasion, the anvil spring 28 applies a side force against the driver blade 36 that is sufficient to overcome the compressed air return force, and the driver blade 36 is pinned or sticks between the spaced-apart chamfers 54, 56 and the backing plate 30.
A second disadvantage of the known nose piece 20 arises from the continuous contact between the driver blade 36 and wedge 34 as the driver blade 34 advances and retracts during a staple driving operation. Thus, the driver blade 36 and wedge 34 are parts that experience wear and, overtime, that wear can be substantial and require replacement of the anvil 22 and/or driver blade 36. Additionally, the wear can cause the degree of curl imparted to the staple to vary from the desired curl.
Therefore, there is a need for an improved nose piece 20 that is less susceptible to driver blade sticking and has less part wear.
The present invention provides a stapler with an improved nose piece that eliminates sticking of the driver blade caused by the anvil spring and therefore operates more reliably and at less cost. Further, the improved stapler nose piece of the present invention allows the driver blade to move past the anvil with minimal or no side force imposed by the anvil spring. Thus, the driver blade advances and retracts past the anvil wedge with only minimal and inconsequential frictional forces between the anvil wedge and the driver blade. Consequently, the wear on the driver blade and anvil wedge resulting from their relative motion is substantially eliminated, thereby reducing stapler maintenance and further reducing costs. In addition, with reduced anvil wear, the flaring of the legs of the staple is more consistent and repeatable over time, thereby providing a consistently high quality clinching of the materials by the staple. Therefore, the stapler of the present invention is more reliable, requires less maintenance and, over time, provides a higher quality, more efficient, and more economical stapling process. The stapler of the present invention is especially useful in clinching materials, for example, fabric and foam, that are used to make a mattress.
According to the principles of the present invention and in accordance with the described embodiments, the invention provides a stapler for clinching materials together with a generally U-shaped staple. The stapler has an anvil with spaced-apart wedges disposed adjacent a backing plate, and the wedges have respective chamfers that contact the legs of the staple and guide the legs away from each other. A biasing element provides a biasing force pushing the wedges of the anvil against the backing plate. A driver blade is movable between the spaced apart wedges and pushes against a staple crown. An actuator is mechanically connected to the driver blade and reciprocates the driver blade through advance and retract motions extending between the backing plate and the anvil. The advance motion advances the driver blade between the spaced-apart wedges, and the driver blade pushes the staple crown over the wedges while curling the staple legs of the staple away from each other. The retract motion retracts the driver blade from between the spaced-apart wedges substantially independent of the biasing force of the biasing element.
In another embodiment, the invention provides an anvil for use in a stapler and in conjunction with a driver blade for clinching materials together with a generally U-shaped staple. The anvil has spaced-apart wedges providing respective chamfers that contact legs of the staple and guide the legs away from each other.
In a further embodiment, the invention provides a driver blade for use in a stapler and in conjunction with an anvil having spaced-apart wedges for clinching materials together with a generally U-shaped staple. The driver blade has a proximal end that receives a force to move the driver blade and an opposite, distal end that is movable between the spaced-apart wedges on the anvil.
In a still further embodiment, the invention provides a nose piece for use in a stapler for clinching materials together with a generally U-shaped staple. The nose piece has an anvil with spaced apart wedges having respective chamfers that contact the legs of the staple and guide the legs away from each other and a driver blade that is movable between the spaced-apart chamfers.
In yet another embodiment, the invention provides a method of operating a stapler that clinches materials together with a generally U-shaped staple and that has the above-described nose piece.
These and other objects and advantages of the present invention will become more readily apparent during the following detailed description taken in conjunction with the drawings herein.